Overview for Normal Capability Analysis

Use Normal Capability Analysis to evaluate the potential (within) and overall capability of your process based on a normal distribution. Using this analysis, you can do the following:

  • Determine whether the process is capable of producing output that meets customer requirements.
  • Compare the overall capability of the process with its potential (within) capability to assess opportunity for improvement.

To perform the analysis, you must specify a lower or upper specification limit (or both) to define your process requirements. The analysis evaluates the spread of the process data in relation to the specification limits. When a process is capable, the process spread is smaller than the specification spread. The analysis can also indicate whether your process is centered and on target. In addition, the analysis estimates the proportion of product that does not meet specifications.

For example, a quality analyst wants to evaluate the capability of a bolt manufacturing process. To satisfy customer requirements, the thread length of the bolts should be within 0.1 mm of the target of 20 mm. The analyst uses a normal capability analysis to evaluate how well the process meets the specifications of 20 ± 0.1 mm, based on a normal distribution of the data.

Note

This analysis includes transformation functions to transform nonnormal data to fit a normal distribution.

Where to find this analysis

To perform normal capability analysis, choose Stat > Quality Tools > Capability Analysis > Normal.

When to use an alternate analysis

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